This invention relates to stylus assemblies and, more particularly, to stylus assemblies adapted for use in a facsimile receiver.
In a facsimile system, information in the form of pictures of alphanumeric matter on a document at an originating location are scanned and electrical signals are produced which correspond to these pictures and alphanumeric matter. These signals are then transmitted over a suitable transmission path to a facsimile receiver which produces a copy or facsimile of the document. The most commonly used paper for purposes of achieving a high quality facsimile or copy is electrosensitive paper which comprises a paper blank which has been coated on one surface with a black graphite material such as carbon black. The carbon black layer is then coated with an electroresistive layer such as titanium dioxide, TiO.sub.2 or zinc oxide, ZnO. The transmitted electrical signals representing the original document are then used to energize a stylus which traverses the paper located at a receiving location, the traversal being made in a predetermined path. The energized stylus selectively burns away the electroresistive layer and, in this manner, the carbon black layer is exposed and patterned into a facsimile of the originating document.
The stylus in a facsimile receiver must comprise a hard conductive material which is capable of riding over the surface of the paper without substantial wear so as to assure that the stylus makes the same mark time after time. One such material is tungsten which is also quite brittle. Since prior art tungsten styli have been unsupported at the marking tip as shown in U.S. Pat. No. 3,761,954, stylus breakage is quite common. Also, stylus wear is quite common.
Another problem associated with prior art facsimile stylus assemblies has been that there may be a danger of electric shock to the operator of the device due to the relatively high voltages employed and the exposed unsupported stylus tip. For example, typical facsimile receiver stylus may operate at as much as 200 volts.
A further problem associated with prior art facsimile systems has been the presence of airborne particulate emissions which emanate from the paper. These emissions have been found to include but are not limited to titanium dioxide, zinc oxide, sodium hydroxide, carbon monoxide, carbon dioxide, oxygen, nitrogen, methane, ethane, propane, butanes, hydrogen sulfide, argon, carbon disulfide, sulfur dioxide, carbonyl sulfide, water vapor, nitric oxide and ammonia in various amounts. Further, it is believed that certain facsimile systems may also produce ozone. While it has not been conclusively determined whether any of these emissions may be toxic to the operator of the device or to persons in the immediate vicinity, the emissions are at least annoying and attempts have been made to reduce them.
Thermal sensitive paper such as that shown in U.S. Pat. No. 3,978,270 is characterized by little or no emissions. However, this paper has not been as widely accepted as conventional electrosensitive paper for various reasons. For example, thermal paper is patterned by varying the temperature of the stylus in proportion to transmitted facsimile signals. Since the stylus temperature may not be varied instantaneously due to its thermal inertia, the stylus must traverse the paper at a speed slow enough to allow its temperature to fluctuate. This speed is not sufficiently high for facsimile use. Accordingly, it would be desirable to provide a facsimile stylus assembly which would operate at low particulate emission levels when using conventional facsimile paper.
A still further problem associated with known prior art stylus assemblies is that irregularities in the paper may cause the stylus to vibrate and this vibration may cause the image produced to deteriorate. Accordingly, attempts have been made to fabricate stylus assemblies having sufficient mass to dampen unwanted vibrations and maintain the stylus in contact with the paper. See, for example, U.S. Pat. No. 3,953,861 to Kipling. Another approach has been to positively bias the stylus assembly against the recording paper by means of a spring. See, for example, U.S. Pat. No. 3,774,229 to Blackwood et al and the styli heretofore used in QWIP Systems 1000 and 1200 facsimile transceiver. See also the aforesaid U.S. Pat. No. 3,761,954 which discloses the use of foil strips with a rubber based adhesive strip to control damping characteristics.